1. Field of the Invention
The present invention relates to a weighing system, and more particularly to a weighing system in which a weighing driving section of each of a plurality of weighing units, a weighing control section for controlling the weighing driving section and the like are coupled through a LAN.
2. Description of the Related Art
Conventionally, a weighing system which functions as a combination scale comprises a plurality of weighing units, each of which includes a hopper, a load cell and the like. Articles (e.g, potato chips) to be weighed are fed to these units and weighed. The weights of the articles in the units are then combined to form combination weights, as will be understood by those familiar with combination scales. A combination weight fully within an acceptable range of weights is selected and the articles in the corresponding weighing units are discharged for delivery to a packer, such as a vertical form-fill-seal machine which operates to pack the measured weight of articles into a bag made by the packer. Each weighing unit is controlled by a weighing control unit comprising a single CPU.
As the number of the weighing units forming the weighing system becomes larger, the number of possible combinations which can be calculated necessarily increases, which increases the load on the CPU. For this reason, a single CPU cannot completely perform in a sufficiently short time all the calculations in some cases. Therefore, a system in which a plurality of CPUs are provided to share the processing is sometimes employed. In some cases where the load is further increased, a weighing system is employed in which a weighing driving section formed by a single CPU is provided for each weighing unit. In a system wherein one weighing driving section is provided for each weighing unit, a weighing control unit having one CPU for controlling the whole combination scale is usually provided. The weighing control unit is connected, through an ordinary serial telecommunication line, to all the weighing driving sections provided on the weighing units.
In systems in which the number of weighing driving sections is predetermined and relatively small, the weighing driving sections are connected to the weighing control units through the serial telecommunication line as described above. However, if the number of the weighing units is increased or the packing speed of the packer is increased, it is impossible to quickly respond to data such as operating conditions or control information between the weighing control section of the weighing control unit and the weighing driving section of the weighing unit. Also, if a program to be executed by the weighing driving section is to be exchanged, updated or the like, it is necessary to exchange the program of all the weighing driving sections. Furthermore, abnormalities of the telecommunication line such as disconnection are found with difficulty if they are caused.